Oxide Semiconductor Memory Cell for Fast Access and Long Retention
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Solution Overview
Problem
Existing semiconductor storage devices, such as DRAM and flash memory, face challenges with data retention time, power consumption, and the need for frequent refresh operations in volatile devices, while non-volatile devices like flash memory suffer from limited write cycles and high voltage requirements.
Innovation Solution
A semiconductor device is proposed with a layered structure incorporating a transistor using an oxide semiconductor and another transistor using a material other than oxide semiconductor. This configuration allows for low off-state current, enabling long data retention without the need for refresh operations and allowing high-speed data writing and reading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a volatile storage device like DRAM is used to store data, then writing and reading operations can be performed quickly, but the data holding time is short and refresh operations are needed at predetermined intervals
Solution Approach 1:
The storage element is divided into two distinct transistors: a first transistor for rapid data writing and a second transistor for data retention. This segmentation allows each transistor to be optimized for its specific function, resolving the contradiction between fast access and long retention.
Solution Approach 2:
The invention changes the material parameter of the second transistor to an oxide semiconductor, which fundamentally alters the off-state current characteristics. This parameter change enables extremely low leakage current, allowing data to be retained without refresh operations while maintaining fast write speeds through the first transistor.
2Duration of action of stationary object
If a non-volatile storage device like flash memory is used to retain data for long time, then refresh operations are not needed, but high voltage is necessary for holding or removing electric charge and writing speed is relatively slow
Solution Approach 1:
The invention changes the material parameter of the retention transistor to an oxide semiconductor, which provides extremely low off-state current without requiring high voltage. This enables long-term data retention similar to non-volatile memory but with standard voltage operation and faster write speeds.
Solution Approach 2:
The invention extracts the data retention function from the main storage transistor and assigns it to a separate second transistor. This allows the main transistor to be optimized for fast writing while the separate transistor handles retention, eliminating the need for high voltage and tunneling current mechanisms.
3Use of energy by stationary object
If a volatile storage device is used, then power consumption can be reduced by not needing permanent storage, but refresh operations increase power consumption and cannot sufficiently reduce it
Solution Approach 1:
By segmenting the storage element into two transistors with different material characteristics, the system achieves ultra-low power consumption during retention through the oxide semiconductor transistor's minimal leakage, while maintaining volatile memory's low power operational state during active use.
Solution Approach 2:
Changing the second transistor to an oxide semiconductor fundamentally changes the power consumption profile by reducing off-state current to extremely low levels, effectively eliminating the need for refresh operations and their associated power consumption while maintaining data retention.
4Duration of action of stationary object
If a flash memory with floating gate is used to store data, then data holding time is extremely long, but the gate insulating layer deteriorates by tunneling current and the storage element stops functioning after a predetermined number of writing operations
Solution Approach 1:
The invention extracts the data retention function from the main storage transistor and assigns it to a separate second transistor made of oxide semiconductor. This protects the main transistor from the deterioration caused by repeated tunneling current, significantly increasing the number of reliable write operations while maintaining long data retention.
Solution Approach 2:
By changing the material parameter of the retention transistor to an oxide semiconductor, the invention eliminates the tunneling current mechanism that causes gate insulating layer deterioration. This enables virtually unlimited write cycles while maintaining extremely long data retention times through the oxide semiconductor's minimal leakage current.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The semiconductor device achieves extended data retention times, reduced power consumption, and high-speed data access without the need for frequent refresh operations or high voltage, making it suitable for applications requiring long-term data storage and rapid data processing.
Implementation Method 1
a second transistor (162) formed using a material other than oxide semiconductor... This configuration allows for low off-state current, enabling long data retention without the need for refresh operations
Data Source
AI summary
An object is to provide a semiconductor device with a novel structure. The semiconductor device includes a first wiring; a second wiring; a third wiring; a fourth wiring; a first transistor having a first gate electrode, a first source electrode, and a first drain electrode; and a second transistor having a second gate electrode, a second source electrode, and a second drain electrode. The first transistor is provided in a substrate including a semiconductor material. The second transistor includes an oxide semiconductor layer.